Conventionally, a winding-type electric storage device has been provided as one of electric storage devices employed in power supplies of various types of equipment and the like. The winding-type electric storage device is provided with an electrode assembly in which a positive electrode plate and a negative electrode plate are wound around a core, current collectors electrically connected to the electrode assembly, and a case in which the electrode assembly and the current collectors are housed.
The electrode assembly is formed into a flat shape. Accordingly, the electrode assembly includes a substantially plane section on an outer circumference thereof. A resin sheet having flexibility formed into a cylindrical shape is employed as the core. The core is formed into a flat cylindrical shape according to the external shape of the electrode assembly (cf., for example, Japanese Patent Laid-Open No. 2003-242970).
A positive-electrode lead portion is formed in a first end portion of the electrode assembly, and a negative-electrode lead portion is formed in a second end portion of the electrode assembly. A current collector fixed onto an inner surface of the case is connected to each lead portion. The electrode assembly is supported inside the case by the current collectors. The substantially plane section of the electrode assembly is in proximity to or contact with the inner surface of the case.
As described above, the electrode assembly is restrained in both a winding-center direction and a direction orthogonal to the winding center direction. Accordingly, it is possible to prevent swaying or movement of the electrode assembly which can be a cause for breakage or damage of the electrode assembly and the like.
In the winding-type electric storage device configured as described above, however, the positive and negative electrode plates may be pushed toward a flat direction if excessive vibration or impact is applied. That is, if excessive vibration or impact is applied, the core may fail to withstand the vibration or impact, since a resin sheet formed into a cylindrical shape is employed as the core. Thus, the electrode assembly as a whole may become compressively deformed in the flat direction. In that case, a gap is formed between the substantially plane section of the electrode assembly and the inner surface of the case. If a gap is present therebetween, the electrode assembly as a whole may sway or move inside the case and may become damaged.